Prazosin Tablets

General Notices

Action and use

Alpha1-adrenoceptor antagonist.

Definition

Prazosin Tablets contain Prazosin Hydrochloride.

The tablets comply with the requirements stated under Tablets and with the following requirements.

Content of prazosin, C19H21N5O4

90.0 to 110% of the stated amount.

Identification

Shake a quantity of the powdered tablets containing the equivalent of 10 mg of prazosin with a mixture of 10 mL of dichloromethane and 10 mL of 0.05m potassium hydroxide, filter the organic layer through absorbent cotton, evaporate to dryness and dry the residue at 60° at a pressure not exceeding 2 kPa for 2 hours. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of prazosin (RS 281).

Tests

Uniformity of content

Tablets containing less than 2 mg and/or less than 2% w/w of prazosin comply with the requirements stated under Tablets using the following method of analysis. Carry out the method for liquid chromatography, Appendix III D, using the following solutions in a mixture of 2 volumes of glacial acetic acid, 2 volumes of water and 96 volumes of methanol.

(1) Shake one tablet for 1 hour in a suitable volume of the solvent to produce a solution containing the equivalent of 0.002% w/v of prazosin, centrifuge and use the supernatant liquid.
(2) 0.0022% w/v of prazosin hydrochloride BPCRS.
chromatographic conditions
(a) Use a stainless steel column (20 cm × 4 mm) packed with silica gel for chromatography (5 µm) (Zorbax Sil is suitable).
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 1 mL per minute.
(d) Use an ambient column temperature.
(e) Use a detection wavelength of 254 nm.
(f) Inject 20 µL of each solution.
mobile phase

0.01% w/v of diethylamine in a mixture of 2 volumes of glacial acetic acid, 2 volumes of water and 96 volumes of methanol.

determination of content

Calculate the content of C19H21N5O4 in each tablet using the declared content of C19H21N5O4 in prazosin hydrochloride BPCRS.

Related substances

Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.

(1) Shake a quantity of the powdered tablets containing the equivalent of 5 mg of prazosin with 2 mL of a mixture of 5 volumes of diethylamine and 95 volumes of chloroform, centrifuge and pass the supernatant liquid through a 0.5 µm PTFE filter.
(2) Dilute 1 volume of solution (1) to 200 volumes with the same solvent.
(3) Dilute 2 volumes of solution (2) to 5 volumes with the same solvent.
chromatographic conditions
(a) Use as the coating silica gel GF254 (Analtech Uniplates are suitable).
(b) Use the mobile phase as described below.
(c) Apply 20 µL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, dry in air and examine under ultraviolet light (254 nm).
mobile phase

5 volumes of diethylamine and 95 volumes of ethyl acetate.

limits

Any secondary spot in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) and not more than two such spots are more intense than the spot in the chromatogram obtained with solution (3).

Assay

Weigh and powder 20 tablets. Carry out the method for liquid chromatography, Appendix III D, using the following solutions in a mixture of 2 volumes of glacial acetic acid, 2 volumes of water and 96 volumes of methanol.

(1) Shake a quantity of the powdered tablets containing the equivalent of 2 mg of prazosin with 100 mL of the solvent mixture for 30 minutes, centrifuge and use the supernatant liquid.
(2) 0.0022% w/v of prazosin hydrochloride BPCRS.
chromatographic conditions

The chromatographic conditions described under Uniformity of content may be used.

mobile phase

0.01% w/v of diethylamine in a mixture of 2 volumes of glacial acetic acid, 2 volumes of water and 96 volumes of methanol.

determination of content

Calculate the content of C19H21N5O4 in the tablets using the declared content of C19H21N5O4 in prazosin hydrochloride BPCRS.

Labelling

The quantity of active ingredient is stated in terms of the equivalent amount of prazosin.